Ziprasidone is an antipsychotic agent with the following chemical name: 5-[2-[4-(1,2-benzisothiazol-3-yl)-1-piperazinyl]ethyl]-6-chloro-1,3-dihydro-2H-indol-2-one of formula (I)

Ziprasidone is disclosed in U.S. Pat. Nos. 4,831,031 and 5,312,925 (assigned to Pfizer). Ziprasidone inhibits synaptic reuptake of serotonin and norepinephrine. No appreciable affinity was exhibited for other receptor/binding sites tested, including the cholinergic muscarinic receptor. The mechanism of action of ziprasidone, as with other drugs having efficacy in schizophrenia, is unknown. However, it has been proposed that this drug's efficacy in schizophrenia is mediated through a combination of dopamine type 2 (D 2) and serotonin type 2 (5HT 2) antagonism. Ziprasidone's antagonism of histamine H receptors may explain the somnolence observed with this drug.
U.S. Pat. No. 5,312,925 (Pfizer Inc.) describes a process for the synthesis of monohydrate of 5-(2-(4-(1,2-benzisothiazol-3-yl)piperazinyl)ethyl)-6-chloro-1,3-dihydro-2H-indol-2-one hydrochloride and its characterization based on IR, XRD and moisture content. The '925 patent also discloses that the hemihydrate may be obtained by the process described in Example 16 of U.S. Pat. No. 4,831,031 and its characterization by IR, XRD and moisture content. It also discloses the IR, XRD and moisture content of anhydrous Ziprasidone hydrochloride. According to the invention in the '925 patent, Ziprasidone of water content of 3.97, 2.55 and 0.37% were used for the IR and XRD study of Ziprasidone hydrochloride monohydrate, hemihydrate and anhydrous. In this invention, the monohydrate of Ziprasidone hydrochloride was prepared by reacting anhydrous 5-(2-(4-(1,2-benzisothiazol-3-yl)piperazinyl)ethyl)-6-chloro-1,3-dihydro-2H-indol-2-one with aqueous hydrochloric acid. The temperature range of the reaction was maintained between 60 to 65° C. and aqueous hydrochloride used for salt formation was around 0.7 M. Depending on the reaction temperature and other conditions, the reaction times were set around 3 to 24 hours. The final product thus obtained was dried carefully in monitored conditions to make certain that water content was from about 3.8% to about 4.5% to obtain the stable monohydrate.
U.S. Pat. No. 6,150,366, discloses a manufacturing process of ziprasidone hydrochloride monohydrate, comprises: 1) dissolving, ziprasidone free base in a solvent comprising THF and water, in a volume ratio of about 22-35 unit volumes of THF to about 1.5-8 volumes of water; 2) heating the solution resulting from step (1); 3) adding HCl to the solution resulting from step (2); and 4) cooling the solution resulting from step (3) and crystals collected by filtration and drying.
U.S. Pat. No. 5,206,366 and U.S. Pat. No. 5,338,846 describe a process for preparing ziprasidone by reacting 1-(1,2-benzisothiazol-3-yl) piperazine with 5-(2-chloroethyl)-6-chloro-oxindole in water with a neutralizing agent such as sodium carbonate under reflux.
J. Med. Chem. 1996, 39, 143-148 discloses preparation of ziprasidone by reacting 1-(1,2-benzisothiazol-3-yl)piperazine with 5-(2-bromoethyl)-6-chloro-oxindole in isoamyl alcohol solvent in the presence of sodium carbonate.
Some salts of ziprasidone, and in particular, its hydrochloride salt is a potent commercial antipsychotic agent useful in the treatment of various disorders, including schizophrenia and anxiety diseases. Ziprasidone hydrochloride is currently marketed under the proprietary name of Geodon. Other salts of ziprasidone are also reported to be effective for the treatment of the same type of diseases.
Some of the processes described in the aforementioned patents necessitate the use of ion-exchange catalyst (i.e. sodium iodide) and/or phase transfer catalysts (for example tetra butyl ammonium bromide or tetra butyl phosphoriium bromide) in order for the coupling reaction producing ziprasidone to take place. For example, U.S. Pat. No. 4,831,031 indicates that arylpiperazinyl-ethyl (or butyl)-heterocydic compounds may be prepared by reacting piperazines of the formula II with compounds of the formula III as follows in [Scheme 1]:
Wherein Hal is fluoro, chloro, bromo or iodo; and Ar, n, X and Y are as defined therein with reference to formula I. According to the '031 patent the coupling reaction is generally conducted in a polar solvent, such as a lower alcohol, dimethylformamide or methylisobutylketone, and in the presence of a weak base and that, preferably, the reaction is carried out in the presence of a catalytic amount of sodium iodide, hydrogen chloride and neutralizing agent such as sodium carbonate.
In some instances, the ziprasidone obtained was purified by column chromatography, thus making the process impractical for large-scale preparations. Another process uses potentially explosive gases such as hydrogen in the presence of catalysts, for example zinc, palladium on carbon, followed by acid treatment to carry out a reduction and cyclization of an intermediate, in order to obtain ziprasidone.
Despite various processes disclosed in the prior art for the preparation of ziprasidone and salts thereof, still there is a need for a good process for producing ziprasidone and pharmaceutically acceptable acid addition salts of ziprasidone thereof, in high purity. One of the major problems faced in the prior art is formation of sticky material and difficult stirrability of the reaction mass. This problem is especially acute in large scale manufacturing.
The present invention provides a process for the preparation of ziprasidone in high yields and purity, suitable for large-scale manufacturing, which helps to overcome some of the deficiencies of the prior art.